I've had a fair bit of experience with Ohlins and Penske shocks, and the statements above don't take into consideration fitness for use, nor a good suspension shop/expert correctly setting up and configuring a shock for your particular usage.

Take my NT650 for example. The Penske model I've got on there at the moment is sold online via several vendors for use with my bike, as well as many other bikes. But what they don't tell you is that the shock internals are built for loads generated by a swingarm that's hooked up to the chassis via a linkage. The NT650 does not have a linkage, it's bolted straight onto the swingarm. The internals supplied in the shock are provided in vanilla format by Penske for the application they most commonly market that model shock for - bikes with linkages. Penske will advise that for an application where the shock is directly attached to swingarm and chassis upgraded internals are required as forces dissipated through the shock at certain points of the swingarm's travel are MUCH higher.

This is why, with Ohlins, buying over the internet via eBay is not always a good idea. Sure, Ohlins has a shock body they specify for use with 20 models of bike, and eBay seller has bolted onto the shock body the mounting hardware for your specific model of bike, but this is not representative of what Ohlins (or a competent Ohlins supplier) would sell you if they had your bike and usage requirements in front of them when they built the shock.

I get my shocks built by a guy who used to race in both the UK and US, he's built shocks for British Supersport teams and a few Irish road racers. He's got over 70,000 hours of riding/tuning/racing under his belt and he knows shocks inside out. He takes a stock Penske/Ohlins/WP shock, and installs the internals applicable to the usage you will be demanding of it.

I found him because, when I installed the Penske I'd bought off eBay on my NT650, it blew and leaked all down the shaft within a few thousand k's. Once the internals were installed that were suitable to the application, the shock's 16,000 k's in and copped an absolute hiding, and not a peep yet from it. All that was required was the 2 or 3 washers Penske sells to solve the problem my bike causes their standard shock.

Ohlins, Penske, WP shocks are extremely customisable. There's a huge range of shims, bearings, seals available for building a shock that will perform and last.

Even cheap sh*t like Showa is perfectly OK when the internals are correctly specified, which is what BMW will have done when they specified exactly what Showa had to provide for the OEM bike.

Which, would probably explain why many of the replacement shocks are dying so fast - they're probably not built to the exact same specs as the ones that shipped on the bike out of the showroom. You're most likely getting the same shock body, but the internals aren't specifically selected to withstand the sort of abuse BMW would have explicitly specified they should on the showroom-shipping unit.